The present invention relates to motion control apparatus and particularly apparatus for controlling small movements of objects with microscopic precision. The invention has particular application in microscopic test and inspection devices, such as that used for testing integraed circuit semi-conductor devices or the like.
Microscopic test and inspection devices typically include a base on which is mounted a microscope, a positioning assembly for supporting and positioning an object under test in the field of view of the microscope, and one or more test probes. The test probes are commonly mounted on a platen which is capable of limited vertical movement. The positioning assembly for the viewed object is capable of X, Y, Z and rotational movements and carries thereon a chuck which has a support surface on which is seated the object under test, such as an integrated circuit in wafer or packaged form.
In integrated circuits, the circuit conductors or other test points which must be contacted by the test probes are extremely minute, having dimensions as small as less than 1 micron. Therefore, the test probes must be positioned with respect to the integrated circuits with extreme accuracy, since contact of the test probe with an unintended part of the integrated circuit could severely damage the circuit or the entire wafer. While this precise positioning can be readily accomplished on the initial positioning of the test probes, it frequently becomes necessary during a test operation to lower the integrated circuit from the predetermined test position contacting the probes, and then return the integrated circuit to the predetermined test position. This must be done with extreme accuracy. In other words, the parts must undergo a vertical separation and repositioning movement without any significant incidental X, Y or rotational movement. This is a significant problem, since all bearings must, of necessity for manufacture, include some irregularities or clearances to permit movement and, therefore, some incidental extraneous movement is unavoidable.
Prior test devices have attempted to solve this problem by the use of precision bearings with extremely close tolerances, but even by the use of such bearings it has been impossible to limit extraneous movement to less than several microns. This degree of precision is inadequate in state-of-the-art integrated circuits, where resolution to less than 1 micron is necessary.
Furthermore, prior motion control devices have been relatively bulky, presenting a high profile, which increases the overall height of the positioning assembly and, therefore, the height of the microscope, to an extent which makes the device difficult for someone to use while sitting in a chair. Also, undesirable vibrations transmitted from the supporting medium are amplified through the height of the positioning assembly.